WO2020178042A1

WO2020178042A1 - Turbomolecular vacuum pump and purging method

Info

Publication number: WO2020178042A1
Application number: PCT/EP2020/054556
Authority: WO
Inventors: Nicolas Varennes; Antoine DENGREVILLE
Original assignee: Pfeiffer Vacuum
Priority date: 2019-03-05
Filing date: 2020-02-20
Publication date: 2020-09-10
Also published as: KR20210134315A; FR3093544B1; TW202040008A; DE112020001075T5; FR3093544A1; CN113518863A; JP2022522883A

Abstract

The present invention concerns a turbomolecular vacuum pump (1) comprising a device for injecting purge gas (21) comprising at least one channel (20) provided in the stator (2) and emerging between the rotor (3) and the stator (2), for injecting a purge gas into the flow path of the pumped gases, downstream from at least one stage of blades (9) of the rotor (3), the device for injecting purge gas (21) being configured such that the flow rate of the injected purge gas is lower than a predetermined threshold such that the difference between the suction pressure (6) without injection of the purge gas and with injection of a purge gas is lower than 0.066 Pa. The invention also relates to a method for purging a turbomolecular vacuum pump (1).

Description

Title: Turbomolecular vacuum pump and purge process

The present invention relates to a turbomolecular vacuum pump and a method for purging the turbomolecular vacuum pump.

The generation of a high vacuum in an enclosure requires the use of turbomolecular vacuum pumps, composed of a stator in which a rotor is driven in rapid rotation, for example a rotation at more than twenty thousand revolutions per minute.

In some processes in which turbomolecular vacuum pumps are used, such as semiconductor or LED manufacturing processes, a deposit layer may form in the vacuum pump. This deposit can lead to a restriction of play between the stator and the rotor which can cause the rotor to seize. The deposition layer in fact heats the rotor by friction, which can generate creep of the latter and then a possible crack.

It is known practice to heat the stator to prevent condensation of reaction products in the pump. However, the stator heating temperature generally cannot exceed 90 ° C, or even 120 ° C, in order to preserve the mechanical strength of the rotor. Heating the stator to these temperatures effectively makes it possible to reduce the formation of deposits in the pump without however always completely preventing it, in particular for certain chemistries, such as for AICI ₃ for example.

Regular maintenances must therefore be scheduled to frequently clean the vacuum pump.

One of the aims of the present invention is to provide a turbomolecular vacuum pump which at least partially resolves at least one drawback of the state of the art.

To this end, the invention relates to a turbomolecular vacuum pump configured to drive gases to be pumped from a suction to a discharge, the turbomolecular vacuum pump comprising:

a stator comprising at least one stage of fins and a Holweck stator in which helical grooves are formed, and

a rotor comprising:

at least two stages of blades, the stages of blades and the stages of vanes succeeding each other axially along an axis of rotation of the rotor in a turbomolecular stage of the turbomolecular vacuum pump, and o a Holweck skirt configured to rotate opposite the helical grooves of the stator in a molecular stage of the turbomolecular vacuum pump located downstream of the turbomolecular stage in the direction of circulation of the pumped gases, characterized in that the turbomolecular vacuum pump further comprises a purge gas injection device comprising at least one channel formed in the stator and opening, for example through at least one hole, between the rotor and the stator, to inject a purge gas into the passage path pumped gases, downstream of at least one stage of the rotor blades, the purge gas injection device being configured so that the flow rate of the injected purge gas is less than a determined threshold so that the difference between the pressure suction without injection of the purge gas and with the injection of a purge gas is less than 0.066 Pa (or approximately 0.5 mTorr).

The pumped gases are thus diluted without or with very little change in the pumping performance at the suction of the turbomolecular vacuum pump.

The partial pressures of the condensable gases can thus be lowered to remain below the condensation values. This limits the risk of deposits in the turbomolecular vacuum pump and extends the time between two maintenances.

Injecting a purge gas downstream of at least one stage of the blades further helps prevent backscattering of the purge gas into the chamber to be evacuated.

Another important advantage is that the lowering of the partial pressure of the gases likely to be deposited in the turbomolecular vacuum pump makes it possible to increase the flow of gas to be pumped for the same set temperature for heating the stator. It is therefore possible to increase the flow of the pumped gases without risk of additional deposits due to the lowering of the partial pressures and without mechanical risks for the rotor.

The turbomolecular vacuum pump may have one or more of the features described below, taken alone or in combination.

At least one channel opens, for example, at the level of the molecular stage, for example through at least one hole.

For example, provision is made for the channel to open into an upper part of the Holweck stator, at the entrance to the molecular stage. The axis of the channel emerges from the Holweck stator at a distance from the turbomolecular stage, for example less than quarter of the height of the Holweck stator. The molecular stage can thus be purged almost entirely.

The channel can also open into a lower part of the Holweck stator, at the outlet of the molecular stage, for example at a distance from the turbomolecular stage greater than half the height of the Holweck stator, in particular for applications where a deposit is found in the lower half of the Holweck stator.

The flow rate of injected purge gas is for example greater than or equal to 0.1689 Pa.m ³ / s (or 100 sccm).

The turbomolecular vacuum pump may further include an additional purge gas injection device configured to inject additional purge gas at the bearings of the turbomolecular vacuum pump located under the Holweck skirt. The additional injection device for a purge gas cools the engine and allows the swivel elements of the turbomolecular vacuum pump to be swept, in particular the bearings, the electrical connections, the welds and the emergency bearings. Scavenging these elements with the additional purge gas protects them from potentially aggressive pumped gases.

For example, the additional purge gas injection device has one or more inlets configured to deliver additional purge gas into a cavity receiving one end of a shaft configured to rotate the rotor.

The flow rate of additional purge gas is for example less than the flow rate of purge gas of the purge gas injection device, such as less than or equal to 0.08446 Pa.m ³ / s (or 50 sccm).

According to an exemplary embodiment, the turbomolecular vacuum pump comprises a common pipe for supplying the device for the additional injection of a purge gas and the channel of the device for injecting a purge gas. It is thus possible to limit the number of connections to the purge gas source on the turbomolecular vacuum pump.

The rotor has for example more than four stages of blades, such as between four and eight stages of blades.

At least one channel opens, for example, at the level of the turbomolecular stage, for example through at least one hole.

The channel opens for example at one of the last three stages of blades in the direction of circulation of the pumped gases. This also avoids possible deposits in the last compression stages of the turbomolecular stage.

A subject of the invention is also a method for purging a turbomolecular vacuum pump as described above, in which the flow rate of the purge gas injected into the passage path for the pumped gases, downstream of at least one stage of blades rotor, is less than a threshold determined so that the difference between the suction pressure without injection of purge gas and with injection of purge gas is less than 0.066 Pa (or approximately 0.5 mTorr).

The purge gas is, for example, nitrogen.

The determined threshold of the flow rate of the injected purge gas is for example 0.76 Pa.m ³ / s (ie approximately 450 sccm).

Presentation of the drawings

Other advantages and characteristics will become apparent on reading the following description of a particular embodiment of the invention, but in no way limiting, as well as the appended drawings in which:

[Fig. 1] shows a schematic view of a turbomolecular vacuum pump according to a first exemplary embodiment.

[Fig. 2] shows an axial sectional view of the turbomolecular vacuum pump of FIG. 1.

[Fig. 3] shows a partial view of a Holweck stator of the turbomolecular vacuum pump of Figure 2.

[Fig. 4] shows a view similar to Figure 2 for a second embodiment.

In these figures, identical elements bear the same reference numbers.

The following embodiments are examples. Although the description refers to one or more embodiments, this does not necessarily mean that each reference relates to the same embodiment, or that the characteristics apply only to one embodiment. Simple features of different embodiments can also be combined or interchanged to provide other embodiments.

The term “upstream” is understood to mean an element which is placed before another with respect to the direction of flow of the gas. Conversely, the term “downstream” is understood to mean an element placed after another relative to the direction of flow of the gas to be pumped, the element located upstream being at a lower pressure than the element located downstream. Figures 1 and 2 illustrate a first embodiment of a turbomolecular vacuum pump 1.

The turbomolecular vacuum pump 1 comprises a stator 2 in which a rotor 3 is configured to rotate at high speed in axial rotation, for example a rotation at more than twenty thousand revolutions per minute.

The turbomolecular vacuum pump 1 comprises a turbomolecular stage 4 and a molecular stage 5 located downstream of the turbomolecular stage 4 in the direction of circulation of the pumped gases coming from a suction 6 of the turbomolecular vacuum pump 1 (represented by the arrows F1 in figure 2). The pumped gases enter through the suction 6, first pass through the turbomolecular stage 4, then the molecular stage 5, to be then discharged to a discharge 8 of the turbomolecular vacuum pump 1. The discharge 8 is connected to a primary pumping.

An annular inlet flange 7 surrounds, for example, the suction 6 to connect the vacuum pump 1 to an enclosure whose pressure is to be lowered.

In the turbomolecular stage 4, the rotor 3 comprises at least two stages of blades 9 and the stator 2 comprises at least one stage of fins 10. The stages of blades 9 and of fins 10 follow one another axially along the axis of rotation ll of the rotor 3 in the turbomolecular stage 4. The rotor 3 comprises for example more than four stages of blades 9, such as for example between four and eight stages of blades 9 (six in the example illustrated in FIG. ).

Each stage of blades 9 of the rotor 3 comprises inclined blades which extend in a substantially radial direction from a hub 11 of the rotor 3 fixed to a shaft 12 of the turbomolecular vacuum pump 1. The blades are distributed regularly around the periphery of the hub 11.

Each stage of fins 10 of the stator 2 comprises a ring from which depart, in a substantially radial direction, inclined fins, distributed regularly around the inner periphery of the ring. The fins of a fin stage 10 of stator 2 engage between the blades of two successive blade stages 9 of rotor 3. The blades of rotor 3 and the fins of stator 2 are angled to guide the molecules of the pumped gas to molecular stage 5.

In molecular stage 5, rotor 3 has a Holweck skirt 13, formed by a smooth cylinder, which rotates opposite helical grooves 14 of a Holweck stator 15 of stator 2 (Figure 3). The helical grooves 14 of the stator 2 make it possible to compress and guide the gases pumped towards the discharge 8 (FIG. 2).

The rotor 3 can be made in one piece (monobloc) or it can be an assembly of several parts. It is for example made of aluminum material. It is fixed to the shaft 12 driven in rotation in the stator 2 by an internal motor 16 of the turbomolecular vacuum pump 1. The motor 16 is for example arranged under a bell 17 of the stator 2, itself arranged under the Holweck skirt 13 of the rotor 3. The rotor 3 is guided laterally and axially by magnetic or mechanical bearings 18. The vacuum pump 1 can also include emergency bearings 19.

The stator 2 is for example made of aluminum material and produced by assembling several parts.

The turbomolecular vacuum pump 1 can also include means for controlling the temperature of the stator 2 to heat the stator 2 to a set temperature, in particular less than 120 ° C, such as 90 ° C.

The turbomolecular vacuum pump 1 further comprises a purge gas injection device 21 comprising at least one channel 20 formed in the stator 2 and emerging between the rotor 3 and the stator 2, to inject a purge gas into the path passage of the pumped gases from the suction 6, downstream of at least one stage of blades 9 (Figures 2 and 3).

The partial pressures of the condensable gases can thus be lowered to remain below the condensation values. This makes it possible to limit the risks of deposits in the turbomolecular vacuum pump 1 and to extend the time between two maintenances.

Injecting a purge gas downstream of at least one stage of blades 9 furthermore makes it possible to prevent backscattering of the purge gas in the chamber to be evacuated.

Another important advantage is that the lowering of the partial pressure of the gases liable to be deposited in the turbomolecular vacuum pump 1 makes it possible to increase the flow of gas to be pumped for the same set temperature for heating the stator 2. It is therefore possible to increase the flow of the pumped gases without risk of additional deposits due to the lowering of the partial pressures and without mechanical risks for the rotor 3.

The purge gas is for example air or nitrogen. The flow rate of injected purge gas is for example greater than or equal to 0.1689 Pa.m ³ / s (or 100 sccm).

The purge gas injection device 21 is configured so that the flow rate of the injected purge gas is less than a determined threshold so that, in operation, the difference between the pressure at the suction 6 of the turbomolecular vacuum pump 1 without injection of purge gas and with injection of purge gas is less than 0.066 Pa (or approximately 0.5 mTorr). The injection of the purge gas into the The passage of the pumped gases thus does not or very little change the pumping performance at the suction 6 of the turbomolecular vacuum pump 1.

For the pumping of gas of intermediate weight, such as nitrogen, the determined threshold of the flow rate of the injected purge gas is for example 0.76 Pa.m ³ / s (ie approximately 450 sccm).

For the pumping of heavier gases, such as argon, the determined threshold of the flow rate of the injected purge gas is for example 1.3512 Pa.m ³ / s (ie approximately 800 sccm).

For the pumping of lighter gases, such as helium, the determined threshold of the flow rate of the injected purge gas is for example 0.06756 Pa.m ³ / s (ie approximately 40 sccm).

The determined thresholds of the flow rate of the injected purge gas thus make it possible not to modify the pumping performance at the suction 6 of the turbomolecular vacuum pump 1.

It is possible to provide several channels 20 formed in the stator 2 opening out around the rotor 3 through one or more holes, for example circular.

The purge gas injection device 21 may further include at least one connector 25 located at the inlet of the at least one channel 20 and outside the stator 2, to connect the at least one channel 20 to a source. of external purge gas. The purge gas injection device 21 may also include a nozzle (or calibrated orifice) or a flow controller to adjust the flow of purge gas.

According to a first embodiment shown in Figures 1 to 3, the channel 20 opens at the level of the molecular stage 5.

For example, it is expected that the channel 20 opens into an upper part of the Holweck stator 15, at the entrance of molecular stage 5 (Figure 3). For example, the axis of channel 20 emerges from the Holweck stator 15 at a distance d from the turbomolecular stage 4 less than a quarter of the height of the Holweck stator 15 (Figure 2).

Molecular stage 5 can thus be purged almost entirely.

The turbomolecular vacuum pump 1 may also include an additional device for injecting a purge gas 22 configured to inject an additional purge gas at the level of the bearings 18 of the turbomolecular vacuum pump 1 located under the Holweck skirt 13.

According to an exemplary embodiment, the device for the additional injection of a purge gas 22 comprises one or more inlets 23, configured to supply a additional purge gas in a cavity 24 receiving one end of the shaft 12 driving the rotor 3 in rotation. The purge gas rises up along the shaft 12, passing through the emergency bearings 19 where appropriate, the bearings 18, the motor 16 and exit from the bell 17 of the stator 2 to circulate between the bell 17 and the Holweck skirt 13, under the Holweck skirt 13, up to the discharge 8 (arrows F2 in FIG. 2).

The additional injection device of a purge gas 22 makes it possible to cool the engine 16 and makes it possible to sweep the pivoting elements of the turbomolecular vacuum pump 1, in particular the bearings 18, the electrical connections, the welds and the bearings. emergency 19. Sweeping these elements with the additional purge gas protects them from potentially aggressive pumped gases.

The flow of additional purge gas is low. It is for example less than or equal to the purge gas flow rate of the purge gas injection device 21, such as less than or equal to 0.08448 Pa.m ³ / s (or 50 sccm). The device for the additional injection of a purge gas 22 may further comprise a nozzle or a flow controller for adjusting the flow rate of the purge gas.

According to an exemplary embodiment, the turbomolecular vacuum pump 1 comprises a common pipe for the supply 23 of the device for the additional injection of a purge gas 22 and the channel 20 of the device for injecting a purge gas 21 so as to limit the number of connections to the purge gas source on the turbomolecular vacuum pump 1. One or more nozzles and / or one or more valves arranged on the inlet 23 and / or the channel 20 can make it possible to differentiate the purge rate of the additional purge rate.

In operation, the purge gases in the passage path of the pumped gases and at the level of the bearings 18 can be injected continuously.

They can also be injected independently. In fact, the device 21 for injecting a purge gas may include a valve to stop / allow the injection of a purge gas. For example, it is possible to cut off the injection of the purge gas in the passage path of the pumped gases when the pumped gases are without risk for the turbomolecular vacuum pump 1 while leaving an injection of purge gas by the additional injection device. a purge gas 22 at the bearings 18 for their protection.

FIG. 4 illustrates a second exemplary embodiment.

In this example, the channel 20 opens out at the level of the turbomolecular stage 4, downstream of at least one stage of blades 9. When the rotor 3 has more than four stages of blades 9, the channel 20 opens, for example, at one of the last three stages of blades 9 in the direction of circulation of the pumped gases F1. For example and as shown in Figure 4, the channel 20 opens from the stator 2 into the turbomolecular stage 4 opposite the fifth stage of blades 9 of the rotor 3, that is to say at the level of the second last stage of blades 9 of the six stages of blades 9.

This also avoids possible deposits in the last compression stages of the turbomolecular stage 4.

Claims

1. Turbomolecular vacuum pump (1) configured to drive gases to be pumped from a suction (6) to a discharge (8), the turbomolecular vacuum pump (1) comprising:

- a stator (2) comprising at least one stage of fins (10) and a Holweck stator (15) in which helical grooves (14) are formed, and

- a rotor (3) comprising:

o at least two stages of blades (9), the stages of blades (9) and the stages of fins (10) following one another axially along an axis of rotation (ll) of the rotor (3) in a turbomolecular stage (4) of the turbomolecular vacuum pump (1), and

o a Holweck skirt (13) configured to rotate opposite the helical grooves (14) of the stator (2) in a molecular stage (5) of the turbomolecular vacuum pump (1) located downstream of the turbomolecular stage (4) in the direction of circulation of the pumped gases (F1),

characterized in that the turbomolecular vacuum pump (1) further comprises a purge gas injection device (21) comprising at least one channel (20) formed in the stator (2) and opening between the rotor (3) and the stator (2), to inject a purge gas into the passage path of the pumped gases, downstream of at least one stage of blades (9) of the rotor (3), the purge gas injection device (21) being configured so that the flow rate of the injected purge gas is less than a determined threshold so that the difference between the suction pressure (6) without injection of the purge gas and with the injection of a purge gas, or less than 0.066 Pa.

2. Turbomolecular vacuum pump (1) according to the preceding claim, characterized in that at least one channel (20) opens out at the level of the molecular stage (5).

3. Turbomolecular vacuum pump (1) according to the preceding claim, characterized in that the axis of the channel (20) opens from the Holweck stator (15) at a distance (d) from the turbomolecular stage (4) less than a quarter the height of the Holweck stator (15).

4. Turbomolecular vacuum pump (1) according to one of the preceding claims, characterized in that the flow rate of injected purge gas is greater than or equal to 0.1689 Pa.m ³ / s.

5. Turbomolecular vacuum pump (1) according to one of the preceding claims, characterized in that it further comprises an additional injection device of a purge gas (22) configured to inject an additional purge gas to the level of the bearings (18) of the turbomolecular vacuum pump (1) located under the Holweck skirt (13).

6. Turbomolecular vacuum pump (1) according to the preceding claim, characterized in that the device for the additional injection of a purge gas (22) comprises one or more feeds (23) configured to bring an additional purge gas in a cavity (24) receiving one end of a shaft (12) configured to drive the rotor (3) in rotation.

7. Turbomolecular vacuum pump (1) according to one of claims 5 or 6, characterized in that the flow rate of additional purge gas is less than or equal to the flow rate of purge gas from the purge gas injection device ( 21).

8. Turbomolecular vacuum pump (1) according to one of claims 6 or 7, characterized in that it comprises a common pipe for the inlet (23) and the channel (20).

9. Turbomolecular vacuum pump (1) according to one of the preceding claims, characterized in that the rotor (3) has more than four stages of blades (9).

10. Turbomolecular vacuum pump (1) according to one of the preceding claims, characterized in that at least one channel (20) opens out at the level of the turbomolecular stage (4).

11. Turbomolecular vacuum pump (1) according to claims 9 and 10, characterized in that the channel (20) opens at one of the last three stages of blades (9) in the direction of circulation of the pumped gases (F1 ).

12. A method of purging a turbomolecular vacuum pump (1) according to one of the preceding claims, in which the flow rate of the purge gas injected into the passage path of the pumped gases, downstream of at least one stage of blades (9) of the rotor (3) is less than a threshold determined so that the difference between the suction pressure (6) without injection of the purge gas and with the injection of a purge gas, is less than 0.066 Pa.

13. The purge method according to the preceding claim wherein the purge gas is nitrogen.

14. Purge method according to one of claims 12 or 13, characterized in that the determined threshold of the flow rate of the injected purge gas is 0.76 Pa.m ³ / s.